Mahoney's position reflects that of the US Conference of Catholic Bishops:
In their 2003 pastoral letter, Strangers No Longer: Together on the Journey of Hope, the U.S. Catholic bishops called for a series of reforms to the broken U.S. immigration system, including: 1) policies to address the root causes of migration, such as global poverty; 2) reform of our legal immigration system, including an earned legalization program, a temporary worker program with appropriate worker protections, and reductions in waiting times in family-based immigration categories; and 3) restoration of due process for immigrants.
The US Conference of Catholic Bishops isn't the entire Church, this position isn't upheld in the Catechism and this is not a statement by the Pope.
What's so difficult to understand about those facts?